Lewis acids are among the most powerful initiators for hydrocarbon conversion reactions. Such catalysts have been used in liquid, gaseous and solid form, and have been supported or immobilized on various polymeric and inorganic substrates, including, for example, silica gel, alumina, graphite and various clays.
Both supported and unsupported Lewis acid catalysts have been used with varying degrees of success for initiating alkylation reactions, in the carbocationic polymerization of olefins, such as isobutene, and in hydrocarbon isomerization and cracking reactions. For example, in copending patent application U.S. Ser. No. 064,688, filed May 20, 1993, now abandoned, incorporated herein by reference, there are described solid state insoluble salt catalysts based on at least one solid state insoluble salt selected from the group consisting of the salts of a strong acid and a Group IIIA-VIA transition metal selected from the group consisting of yttrium, lanthanum, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten. Solid state catalysts have been studied for use in the carbocationic polymerization of olefins; a number of these catalysts have been based on the use of a catalyst on a polymeric substrate.
U.S. Pat. No. 4,116,880 discloses a catalyst comprising a fluorinated graphite support having certain Lewis Acids bonded thereto. The Lewis Acids are selected from the halides of the metals of Group IIA, IIIA, IVB, VA, VB or VIB. This patent also discusses superacid catalysts which are supported, for example, on fluorinated alumina, on inert polyfluorinated polymer supports such as polytetrafluoroethylene (Teflon), or on fluorinated polycarbon (coke). The catalysts based on fluorinated alumina are said to show limited adherence of the catalyst to the surface.
U.S. Pat. Nos. 4,719,190, 4,798,667 and 4,929,800 disclose hydrocarbon conversion catalysts prepared by reacting a solid adsorbent containing surface hydroxyl groups with certain Lewis acid catalysts in halogenated solvent. The Lewis acids disclosed as useful in the reference are limited to aluminum and antimony halides and the resulting reaction product is the final catalyst of the invention.
However, in spite of the advances made in the field of hydrocarbon conversion catalysis relating to Lewis acids, there continues to be interest in developing highly efficient catalyst systems which can be recycled or reused in such processes, e.g., in cationic polymerization, alkylation, isomerization and cracking processes. The present invention was developed pursuant to this interest.